1. Technical Field
The present invention is directed toward rotating electric machines having a rotor.
2. Description of the Related Art
This invention relates to an alternating current generator of the Lundell type that has a pair of rotor segments provided with interleaved pole teeth or fingers and a rotor core that carries a field coil. In a common, conventional, thirty-six stator tooth, twelve rotor pole 3-phase configuration, a rotor tooth 10 is fashioned so that it is in a generally trapezoidal shape, having a base 12, a tip side 14 opposite the base 12, and leading and trailing edges 16 and 18, as shown in FIG. 1. The direction of movement of rotor teeth 12 relative to stator teeth 20 is shown by arrow 22. In such a configuration, the base 12 has a length of about three stator slot pitches, with each of the leading and trailing edges sloping about one slot pitch. However, an AC generator of the type having teeth 10 exhibits a magnetic sound that is produced during operation, which may be found objectionable depending on the circumstances.
One approach taken in the art to reduce magnetic noise involves skewing the leading edge in the direction of movement, as also shown in FIG. 1, with the rotor tooth now having leading and trailing edges 24 and 26. The centerline of the tooth, rather than bisecting both the base and tip each into roughly equal halves, is moved toward the leading edge of the rotor tooth.
Another approach taken in the art to reduce magnetic noise is seen by reference to U.S. Pat. No. 4,201,930 to Inagaki et al. Inagaki et al. disclose a claw tooth rotor having irregular trapezoidal shaped teeth wherein the tip is displaced in the direction of the rotation of the rotor.
There is a need, however, for continuous reductions in the level of magnetic noise produced by AC generators, particularly those used in an automotive vehicle, while maintaining or improving electrical efficiency of the generator.
There is therefore a need for an improved alternator and/or portions thereof that minimize or eliminate one or more of the problems as set forth above.
An object of the present invention is to provide a solution to one or more of the problems set forth in the Background.
One advantage of the present invention is that an improved rotor pole shape suitable for incorporation into an AC generator is operative to reduce magnetic noise and improve performance during operation. Another advantage, in a preferred embodiment, is that of providing reduced magnetic noise, while only requiring the use of six diodes in a rectifying portion of an AC generator having a 12-pole rotor, 72-slot stator using a distributed 3-phase winding, rather than 12 diodes for a like generator having two sets of windings.
According to the invention, an alternating current (AC) generator is provided that includes an armature core having a plurality of teeth separated by intervening slots spaced according to a slot pitch. The generator includes at least one multiphase winding disposed on the armature core, and a rotor disposed in the armature having a plurality of pairs of rotor poles, each pair respectively configured for energization in opposite magnetic polarity, the poles comprising a trapezoidal shape having a base, a leading side, a trailing side, and a tip side, wherein the leading side has a plurality of portions. In a preferred embodiment, optionally, the leading side has a first portion extending from the tip (toward the base) sloping at a first rate and a second portion extending away from the first portion (also toward the base) sloping at a second rate less than the first rate. More preferably, the first portion slopes between about one and two slot pitches and the second portion slopes between about one-half and one and one-half slot pitches.